During intermediate vehicle stops such as at a traffic light, an engine may idle for some time. In order to increase fuel efficiency and improve emissions quality, the vehicle engine may be equipped with a start-stop function to reduce prolonged idling by temporarily shutting down the engine and then restarting the engine when restart conditions are met. As the engine is shut down and then subsequently restarted, there may be changes in engine sound during engine spin-down, engine rest, and the engine spin-up. Such perceivable changes in engine sound may be objectionable to the operator, at least because the operator may be expecting a different sound.
Various approaches are provided for suppressing changes in engine sound during engine start-stop operations. In one example, as shown in U.S. Pat. No. 9,347,388, Bohn et al. teaches, playing a predetermined and/or customizable sound through a vehicle audio system during the period that the engine is stopped. The background sound may mask changes in engine noise during engine stop and subsequent engine restart. The volume of the background sound may be increased prior to engine restart to blend the background sound with the sound of the engine start.
However, the inventors herein have recognized potential issues with such systems. As one example, any perceivable change in engine sound during the start-stop operation of the engine may be objectionable to the operator. As another example, increasing the volume of the background noise may not be able to seamlessly mask the sound of the engine shutdown or restart. In particular, during engine spin-down, the engine sounds audible to the operator may vary until the engine has completely stopped spinning. Similar variations in the audible sound may occur immediately after engine restart until a target speed is reached. Such variations may not be effectively masked by playing a background noise whose volume is adjusted. Engine start-stop operations may be frequently used during city drive and such recurring changes in engine sound may degrade the operator's driving experience.
In one example, the issues described above may be addressed by a method comprising: during an idle-stop, generating, through an electronic speaker, an engine sound responsive to an automatic engine stop during each of an engine spin-down and while the engine is subsequently at rest, including commencing at least partial active engine noise cancellation upon the spin-down and ending said cancellation upon reaching stabilized idle in a subsequent restart. In this way, by selectively modifying a recorded engine sound and playing modified versions of the recorded sound during an engine idle-stop and a subsequent engine restart, perceivable changes in engine sound during engine idle-stops may be reduced.
As one example, in response to idle-stop conditions being met (such as in response to a longer than threshold duration of engine idling), an engine idle-stop may be initiated and engine combustion may be suspended. During the idle-stop, a modified version of a recorded or a modelled sound may be played via a dashboard speaker. If the engine idling speed immediately prior to suspension of combustion is lower than a threshold speed, the engine sound audible to the vehicle operator may be recorded using a microphone located in the dashboard of the vehicle and uploaded to a database of the vehicle controller. The database may include recordings of engine sound made at different engine speeds and engine temperatures. Upon suspension of combustion, an inherent engine spin-down sound may be modelled based on the idling speed immediately prior to suspension of combustion. Once the combustion is suspended, engine sound recorded immediately before the idle-stop or an engine sound recording retrieved from the database may be played via a speaker in the dashboard of the vehicle. During engine spin-down, the phase and amplitude of the waveform of the recorded engine sound may be adjusted to cancel the inherent engine spin-down sound and produce an overall residual sound that mimics the engine idling sound prior to suspension of combustion. An unmodified version of the recorded sound may be played during the time that the engine is at rest. Upon a subsequent engine restart, the waveform of the recorded engine sound may be modified to cancel the inherent engine spin-up sound and to maintain an engine idling sound. For example, during the engine restart, the phase of the waveform of the recorded engine may be synchronized with the phase of the inherent engine spin-up sound so that the recorded sound may be gradually phased out by the time the engine speed reaches the target idling speed. Responsive to a higher than threshold torque demand, at restart, playing of the recorded sound may be discontinued at the end of the engine spin-up phase.
In this way, during an engine idle-stop and subsequent restart, by cancelling the inherent engine spin-up and engine spin-down sounds and playing an engine idling sound, changes in engine sound during engine start-stop operations may not be perceived by the operator. In particular, the operator may perceive a continuous engine idling sound during the start-stop operation, even as the inherent engine sound changes. By recording engine sound using a dashboard microphone, immediately prior to engine shut-down, and by playing back a suitably modified version of the recorded sound during engine idle-stop, there may not be any significant difference in the quality of engine sound as audible to the vehicle operator. The technical effect of aligning the phase of a modified recorded sound played during engine spin-up with the phase of an inherent engine spin-up sound is that the same engine sound may be continued until the engine is restarted. By gradually phasing out the recorded engine sound upon engine restart, any abrupt change in engine sound may be unperceivable to the operator. In this way, the overall drive experience of the operator during engine start-stop operations is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.